In the field of kinetic control of a vehicle, a behavior control art such as vehicle stability control (VSC), vehicle dynamic integrated management (VDIM), or the like, which improves the stability of the behavior of a turning vehicle in a yaw direction thereof through electronic control of the action of a braking/driving system or a steering system, is described in Japanese Patent Application Publication No. 2004-306662 (JP-A-2004-306662) or Japanese Patent Application Publication No. 2005-206075 (JP-A-2005-206075). In this VSC, when the behavior of the vehicle may be destabilized, the slip rates or slip amounts (hereinafter referred to as the slip rates or the like) of tires of respective wheels or the steering angles of the wheels are adjusted. Otherwise, the output of an engine or a motor is reduced or limited to restrain the vehicle from being accelerated. When a difference in braking/driving force between the right wheels of the vehicle and the left wheels of the vehicle is created or when the steering angles of the wheels are adjusted, a yaw moment is generated around the center of gravity of the vehicle. When the turning direction of the vehicle is thus changed and the vehicle speed is reduced, the lateral force required for the turning of the vehicle decreases. Therefore, the adjustment of the slip rates or the like of the respective wheels or the steering angles of the wheels and the limitation on acceleration of the vehicle or deceleration of the vehicle restrain the vehicle from behaving unstably, for example, spinning. As a result, the behavior of the vehicle in the yaw direction is stabilized.
In the behavior control as described above, more specifically, turning state quantities representing a turning state of the vehicle, for example, a spin state quantity or a skid state quantity as a function of a vehicle body slip angle or the like, an over-steer state quantity, an under-steer state quantity, and the like are referred to as indexes of the behavior of the vehicle. When these indexes deviate from values assumed in the stably running vehicle or exceed predetermined thresholds respectively, behavior stabilization control, namely, the creation of a yaw moment for stabilizing the behavior of the vehicle (behavior stabilization yaw moment), the limitation on acceleration of the vehicle, or deceleration of the vehicle is carried out. However, there may be a time delay between a time point at which the turning state quantities representing the behavior of the vehicle exceed the thresholds or predetermined ranges respectively and a time point at which the adjustment of the slip rates or the like of the respective wheels for behavior stabilization control (wheel slip control), automatic control of the steering angles of the wheels, or the control of a braking/driving device is started. Thus, in Japanese Patent Application Publication No. 2004-306662 (JP-A-2004-306662), the addition of derivatives of the turning state quantities or derivatives of some of the turning state quantities to the indexes of the behavior of the vehicle with a view to more swiftly restraining the behavior of the vehicle from tending to be destabilized is disclosed. A derivative of each quantity representing the behavior of the vehicle is a first order advance amount of the quantity representing the behavior of the vehicle. Therefore, the aforementioned time delay can be compensated for by adding those derivatives to the indexes for performing behavior stabilization control.
In vehicle behavior control disclosed in Japanese Patent Application Publication No. 2005-206075 (JP-A-2005-206075), a spin state quantity K1·β+K2·dβ/dt . . . (A) as a linear sum of a vehicle body slip angle and a derivative of the vehicle body slip angle is referred to as an index of the behavior of the vehicle, namely, as a control amount in the control for restraining the vehicle from spinning (spin restraint control). It should be noted herein that K1 and K2 are weighting coefficients. This spin state quantity is a quantity equivalent to a yaw moment needed to return the vehicle body slip angle to 0. However, when behavior stabilization control is started referring only to this quantity, there may be caused a time delay as mentioned already: